The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old.
Answer:
lack of resources, and mating
Explanation:
they may go ictenct
Answer:
The letters of DNA pair up because they form hydrogen bonds: each contains hydrogen atoms, which are attracted to nitrogen or oxygen atoms in their partner
Explanation:
Answer:
d. UAC
Explanation:
An anticodon, present on tRNA, is the complementary sequence to a determined codon on the mRNA. tRNA is responsible for placing the aminoacids in the correct order when a protein is being translated, and it does so by complementary binding the codons on the mRNA. Each tRNA can hold a different aminoacid, so, for example, the codon AUG encodes the aminoacid methionine, and this means that only a tRNA that has an anticodon with the sequence UAC will be able to hold metionine and place it on its position on the protein sequence.
Answer:
B. secrete granzymes and perforin.
Explanation:
Perforins are the proteins that perforate the plasma membrane of the target cell and lead to bursting of cells due to holes formed in its membrane. Granzymes are the proteolytic enzymes. They serve to stimulate the target cells to kill themselves by the process of apoptosis.
Binding of natural killer cells to their target cells stimulate the release of granules that are filled with perforins or granzymes to kill the target cells.
Likewise, cytotoxic T cells bind to the infected body cells and release the granules filled with perforins or granzymes to kill those infected cells.
